どんな状況かがよくわかりませんって英語でなんて言うの？

In the situation where you understand the words and what is being said, but you are unsure why it was said, then you may talk about the context or situation - or scene or scenario or 'what is actually happeneing.' You could explain to your teacher that you you are unsure about the context.
"What's going onj in this scenario?" for example.

"I know the words in the sentence but I do not understand it." This explains to the person that you recognise the words in the sentence but you do not understand what the sentence means.

"I know what you mean but I don't know how it feels." This explains to the person that you know what they are saying but you have never been in that situation so cant understand it.

The two sentences you see provided above are great ways to express to your teacher that you know the meaning of the words but you do not understand the meaning of the sentence. In the first sentence you will see the adjective sure and in the second sentence you will see the adjective certain. Both of these words mean to understand something completely.

It is quite common to understand the vocabulary in a sentence but misinterpret the meaning and you are not sure why certain words fit into it instead of others. When we say we don't get something, we mean we don't understand. You can't get your head around it.

example
"I couldn't understand the context".
or
"i don't understand the frame of reference."
or
"i am not familiar with these circumstances,
can you explain the context".

Native speakers will say like this: “I understand the words but I don't understand the meaning of the sentence”.
There are lots of other ways to say it, but this one is the most accurate and most commonly used.
Here is an example on how to use this in a conversation:
A: Is everything clear in this excercise?
B: Not really, teacher. I understand the words but I don't understand the meaning of the sentence. Can you explain it to me, please?

I can understand the meaning of the words but I am unclear about the meaning of the sentence.

This is a simple sentence that means that you can understand the words by themselves, but not the meaning of the sentence.

If you want to explain that you understand the words then you can say 'I know what the words mean' or 'I understand what the words mean'
if you know what something means then you can say you understand it as well.
All the above sentences would be a good way of explaining what you mean